Microhardness Of Ceramics Research Articles

Preparation and Mechanical Characteristics of Multicomponent Ceramic Solid Solutions of Rare Earth Metal Oxides Synthesized by the SCS Method

A study into the use of the Solution Combustion Synthesis (SCS) method with glycine and citric acid to synthesize fine powders of multicomponent solid solutions of oxides of rare earth (RE) metals (Nd, Sm, Eu, Gd, Dy, and Ho) for the preparation of ceramic materials is presented. Synthesis parameters of 4-, 5-, and 6-component entropy-stabilized rare earth oxides (REOs) with a C-type cubic structure are determined. The stability of entropy-stabilized oxides (ESOs) with a C-type structure is shown to depend not only on heavy RE metal quantity, but also on the rate of heating/cooling of the samples. The temperature of the polymorphic transformation of C-type REO structures into B-type (monoclinic) or H-type (hexagonal) structural variants can be described by the equation T (°C) = 0.0214Vcr2 − 62.737Vcr + 46390, where Vcr is the unit cell volume of an oxide with a C-type structure regardless of the number of cations in the solid solution. High-temperature thermal analysis up to 1250 °C revealed that dispersed powders, which contain impurities of basic carbonates along with hydroxocarbonates of RE metals and X-ray amorphous carbon formed during SCS reactions, also react with air moisture during storage. The influence of the ESO phase and cationic composition on the morphology, porosity and microhardness of ceramics was studied. Higher-entropy oxides form samples with higher density, microhardness and a smaller size of particle agglomerates.

Wear and Microhardness of Three Different Types of CAD/CAM Ceramic Materials

Objective: Wear and microhardness of three different types of CAD/CAM ceramics against enamel as an occlusal antagonist were studied. Also, microhardness was evaluated. Materials and Methods: The three tested ceramics were: Vita Enamic (polymer-infiltrated ceramic), IPS e.max CAD (lithium disilicate ceramic) and Celtra Duo (Zirconia reinforced lithium silicate ceramic). The occlusal antagonists were extracted teeth. Thirty samples were constructed divided into 3 groups according to the type of ceramic used (10 samples each). Then each group was subdivided into 2 subgroups (5 samples each), The first subgroups underwent a microhardness test while the other subgroups were first weighed then subjected to wear test and finally re-weighed again before being subjected to microhardness test. Results: The results showed a significant difference in weight loss due to wear between Vita Enamic and both IPS e.max CAD and Celtra Duo. There was also a significant difference for the antagonist tooth structure as regard both weight and height loss between Vita Enamic and both IPS e.max CAD and Celtra Duo. Microhardness results showed a significant difference between Vita Enamic and both IPS e.max CAD and Celtra Duo as regard microhardness without and after wear. For all the tested ceramics, there was no significant difference as regard microhardness without and after wear test. Also, there was no significant difference as regard wear and microhardness between IPS e.max CAD and Celtra Duo.Conclusions: Vita Enamic showed the worst wear behavior and the least abrasiveness to enamel while, IPS e.max CAD and Celtra Duo showed comparable wear behavior and abrasiveness to enamel. Also, ceramic microhardness was not affected by wear for the three tested ceramics.

Physical characteristics of ceramic/glass-polymer based CAD/CAM materials: Effect of finishing and polishing techniques.

PURPOSEThe aim of this study was to compare the effect of different finishing and polishing techniques on water absorption, water solubility, and microhardness of ceramic or glass-polymer based computer-aided design and computer-aided manufacturing (CAD/CAM) materials following thermocycling.MATERIALS AND METHODS150 disc-shaped specimens were prepared from three different hybrid materials and divided into five subgroups according to the applied surface polishing techniques. All specimens were subjected up to #4000 grit SiC paper grinding. No additional polishing has been done to the control group (Group I). Other polishing procedures were as follows: Group II: two-stage diamond impregnated polishing discs; Group III: yellow colored rubber based silicone discs; Group IV: diamond polishing paste; and Group V: Aluminum oxide polishing discs. Subsequently, 5000-cycles of thermocycling were applied. The analyses were conducted after 24 hours, 7 days, and 30 days of water immersion. Water absorption and water solubility results were analyzed by two-way ANOVA and Tukey post-hoc tests. Besides, microhardness data were compared by Kruskal-Wallis and Mann-Whitney U tests (P<.05).RESULTSSurface polishing procedures had significant effects on water absorption and solubility and surface microhardness of resin ceramics (P<.05). Group IV exhibited the lowest water absorption and the highest microhardness values (P<.05). Immersion periods had no effect on the microhardness of hybrid ceramic materials (P>.05).CONCLUSIONSurface finishing and polishing procedures might negatively affect physical properties of hybrid ceramic materials. Nevertheless, immersion periods do not affect the microhardness of the materials. Final polishing by using diamond polishing paste can be recommended for all CAD/CAM materials.

Different-Oxides Nanoceramics Microhardness

With help of the method of the spark plasma sintering (SPS), the fine-grained (of micron approximately) ceramics based on various alumina nanopowders had created. A comparison of microhardness of ceramic samples obtained from 11 alumina nanopowders and 2 their composites was held. Microhardness of the ceramics obtained both by SPS, and by the traditional method (at successive pressing and sintering) is compared. The dependence of ceramics microhardness on the phase composition of the initial nanopowder and the average size of its particles was investigated. Besides alumina nanopowders ( Al 2 O 3), there were compared microhardness of ceramics from other 10 nanopowders of oxides ( SiO 2, ZnO , Fe 3 O 4, Gd 2 O 3, CuO , WO 3, TiO 2, Y 2 O 3, ZrO 2, MgO ) obtained both by SPS, and by the traditional method. It is obtained that the microhardness of the ceramics created on the method of the spark plasma sintering, is significantly higher than a microhardness of the ceramics obtained by the traditional method; at the SPS method the average size of grain in ceramics decreases (to 1 micron and less).

Microhardness of ceramics produced from different alumina nanopowders by different techniques

Fine-grained ceramics (with a grain size on the order of a micron) have been produced by the spark plasma sintering (SPS) of various alumina nanopowders. We have compared the microhardness of ceramic samples prepared from 11 alumina nanopowders and that of composites based on such powders. The ceramics have been prepared by both SPS and a conventional technique (sequential pressing and sintering). We examine the effect of the phase composition and average particle size of the starting nanopowder on the microhardness of the ceramics.

Corrosion effect on the flexural strength &amp;amp; micro-hardness of ips e-max ceramics

Objectives: The effect of ceramics construction (press- able, machinable) and corrosion on flexural strength and micro-hardness was studied. Materials & Methods: Two types of ceramics were tested: IPS e-max Press and IPS e-max CAD. Forty samples were constructed and divided into 2 groups according to the type of ceramics. Each group was then subdivided into 2 subgroups. Subgroups 1 were not subjected to corrosion while subgroups 2 were subjected to corro-sion test. Finally each subgroup was divided into 2 classes according to the type of test: biaxial flexural strength, micro-hardness. Results: There was a sig-nificant difference between the two tested ceramics as regard weight loss as IPS e-max CAD recorded less weight loss than IPS e-max Press. As regard the flex-ural strength, IPS e-max CAD recorded significant higher strength than IPS e-max Press. Corroded sam- ples recorded significant lower flexural strength than non-corroded samples for the two tested ceramics. As regard the Vickers micro-hardness test, the results showed significant difference between the two tested ceramics. IPS e-max CAD recorded higher mi-cro-hardness values than IPS e-max Press. The results also showed that the corroded samples recorded no significant micro-hardness values than non- corroded samples for the two tested ceramics. Conclusions: IPS e-max CAD recorded less weight loss weight loss after being subjected to corrosion test than IPS e-max Press. The method of fabrication affected the flexural strength &micro-hardness of ceramic as machinable ceramic (e-max CAD) recorded significant higher data than pressable ceramic (e-mas Press). Corrosion decreased the flexural strength of both tested ceramics but had no effect on micro- hardness.

Supermicrohardness in ceramics based on nanodisperse alumina powders with additives of magnesia and silica nanopowders

Fine-grained corundum-based ceramics have been obtained by pressing and subsequent sintering a mixture of nanodimensional alumina (Al2O3), magnesia (MgO) and silica (SiO2) powders. The structure and properties of the obtained ceramics have been studied by scanning electron microscopy, scanning probe microscopy, and X-ray diffraction analysis. It is established that the modifying additive of nanodisperse silica (0.05%) produces an almost 40% increase in the microhardness of ceramics.